This invention relates to a foldable wheelchair and more particularly to a wheelchair having a rigidly supported seat and an extended wheelbase when unfolded.
Wheelchairs that are adapted to fold transversely are well known in the art and commonly employ an X-frame structure which is disposed intermediate a pair of sides, spacing the sides apart and providing a base upon which a collapsible seat may be mounted. The X-frame type of wheelchair folds in a transverse direction only and is therefore committed to a structure having a fixed wheelbase dimension. The wheelbase of the chair is generally kept as small as possible in order to provide a wheelchair of compact dimensions. However, as a result of the shorter wheelbase, the wheelchair tends to tip easily onto its front footrests. A further drawback resulting from the shorter wheelbase occurs in that the chair is caused to tilt back to an unstable position when attempts are made to climb small curbs and steps. Additionally, since pairs of front and rear wheels are generally used, on rough terrain one of the rear wheels can lift up and lose contact with the ground, thus making it impossible for a person seated in the chair to propel it or to apply effective braking action.
Another form of foldable wheelchair structure that is known in the art avoids some of the problems encountered with the X-frame wheelchair structure. This wheelchair structure is typified in U.S. Pat. No. 909,411, Hockney, issued on Jan. 12, 1909. The Hockney patent describes a wheelchair with a pair of side-frames that are interconnected by means of a split seat having a hinged centre joint and outer ends which are hingedly connected to the side frames. A hinged split axle together with a hinged split brace transversely interconnect the side frames and a central rigid reach interconnects the intermediate joints of the axle and brace. A free end of the reach carries a single pivotally mounted wheel at the rear of the wheelchair. The chair is folded transversely and the wheelbase distance between the rear wheel and the propelling wheels, which are forwardly set on the wheelchair frame, is reduced by pushing the reach into the frame structure, causing the axle and brace to fold rearwardly and the split seat to fold downwardly. Latching members are provided to prevent accidental collapse of the wheelchair during periods of use.
It may be seen that the Hockney wheelchair provides a structure having an extended wheelbase. However, the problems of stability when climbing curbs and other raised obstructions are not overcome by Hockney in view of the forward placement of the propelling wheels and the rearward location of the single castor wheel. Thus, it may be expected that instability occurs when the front wheels are raised as when traversing an obstacle and the weight is shifted back over the single castor wheel.
A further problem that may be expected with the Hockney wheelchair may be seen in the central hinge structure of the split seat. Thus, the integrity of the seat as a weight supporting member depends entirely on the strength of the hinge and the strength of the means used to connect the hinge to the seat.